I had something similar to this happen a few times smoking and I really do believe it's about the smoking technique.

Are you sure you are not burning the substance (the fact that you are using a rather high dose without breaking through  seems to further suggest this)? Have you tried using a lot more steel screens in the GVG?

Once I tried to change my smoking technique I didn't have any problem anymore. I also had this problem with trying to smoke other substances like tobacco, so you shouldn't worry that an entity is trying to kill you, what you are experiencing has more to do with how you are smoking the substance/burning it and less about the experience on the substance itself, in my opinion.

A combination of some effects of the dmt combined with burning the substance can lead to experiences similar to what you are describing.

Try changing the smoking method and let us know.

Also, use lower doses for the first times. Only once you are sure that you are getting the technique right you should use progressively higher doses. You don't want to rush into this.